Apparatus and method for reducing impurities

Abstract

The invention relates to a device (100) and a method for reducing impurities (V) in a plastic melt (K), in particular in a plastic melt of thermoplastic material. The device comprises a plurality of openings (20) with bridges (21) between them. A cutting edge (22) is formed on the bridges (21).

Description

Technical Field

[0001] This invention relates to an apparatus and method for reducing impurities in plastic melts, particularly in thermoplastic materials. Background Technology

[0002] Many plastic containers are known from the prior art. Various methods for producing these plastic containers, particularly plastic bottles, are known, and the application of these methods depends particularly on the plastic used. Typically, plastic containers are produced in a blow molding process, in which the plastic container (e.g., a plastic bottle) is inflated into its final shape by overpressure in a blow mold.

[0003] In the case of blow molding, different process technologies should be distinguished, among which extrusion blow molding, injection blow molding, and injection stretch blow molding should be mentioned in particular. In extrusion blow molding, a single or multiple layers of plastic tubing are thermally extruded, introduced into a blow mold, and inflated via a blow mandrel introduced into the mold cavity to form a plastic container.

[0004] Injection blow molding is a combination of injection molding and blow molding. In this case, a preform is first produced in an injection mold during the injection molding process. The preform is demolded from the injection mold, optionally shaped, and introduced into the mold cavity of a blow mold, where the preform is finally over-inflated according to the shape pre-given by the mold cavity.

[0005] In injection stretch blow molding, during the blow molding process, the preform introduced into the mold cavity is further stretched using a stretch mandrel. Inflation of the preform can be performed directly after its production by injection molding.

[0006] In alternative production methods, further processing of the preform can also be carried out separately from the production of the preform in space and / or time. Finally, it should be noted that the preform can also be manufactured during extrusion or during extrusion blow molding.

[0007] Typically, the raw material is supplied as granules, heated and melted in an extruder, and then fed into a blow molding tool or injection molding tool. In this tool, the melt is further processed by extruding tubular preforms or by injection molding to form preforms.

[0008] As the population continues to grow, the world's natural resources are becoming increasingly scarce. At the same time, increasing demand leads to greater environmental pollution from waste. Therefore, efforts have been made to repeatedly reuse used packaging. One method of reuse is recycling.

[0009] Many plastics can be reused multiple times. However, this is contingent on these materials maintaining high quality during recycling, or at least a high level of purity before reuse. Therefore, efforts are being made to place recycling equipment directly upstream of production facilities, thereby preventing, for example, recontamination during the transport of recycled (also known as regenerated) pellets. However, such solutions are very expensive and require a high degree of process reliability.

[0010] In the recycling process, the collected used containers are typically separated according to their composition and then shredded. A washing process is also usually performed to clean the material and separate it from foreign substances as much as possible. These shredded plastics are then melted and the molten material is filtered. The filtered melt is then cooled and processed into granules. These granules are then typically filled into bags for transport.

[0011] It is also possible that the varying quality of recycled plastics could result in non-uniform particles with correspondingly different properties.

[0012] All of these factors can lead to defects or impurities that are detrimental to the subsequent blow molding process. Defects, in particular, can cause blow-molded plastic containers to leak or burst during the blow molding process itself or during subsequent filling. This results in machine downtime and potentially high cleaning costs. Summary of the Invention

[0013] Therefore, the object of the present invention is to overcome at least one of the disadvantages of the prior art. In particular, a method and / or apparatus should be provided that enables the production of high-quality plastic containers and reduces the defect rate of plastic containers. Specifically, the reliability of the blow molding or filling process should be improved.

[0014] This objective is achieved by the apparatus and method defined in the independent claim. Further embodiments are derived from the dependent claims.

[0015] In particular, the claimed invention reduces defects in containers, which in turn means that machine downtime caused by leakage or bursting of plastic containers at defects can be reduced or at least minimized during the production of plastic containers.

[0016] The apparatus according to the invention for reducing impurities in molten plastic, particularly in thermoplastic materials, has a plurality of openings with bridging members between them. Cutting edges are formed on the bridging members. These cutting edges are arranged against the flow direction of the molten plastic. Therefore, as the molten plastic flows through the apparatus, impurities present in the molten plastic impact these cutting edges.

[0017] In the current context, thermoplastic materials can be conventional or bio-based polyesters or polyolefins, particularly colored or uncolored PET, copolymers of PET, PEF, HDPE, and PP, wherein the material is recycled or a mixture of virgin and recycled materials. Thermoplastic materials can also be purely virgin materials.

[0018] In this article, impurities are basically understood as three categories of problems or defects that lead to blow-molded container bursting and / or blow-molded container leakage.

[0019] Bursting containers can lead to extended downtime in production facilities because each incident requires some degree of cleaning. Leaking bottles pose a risk of slow leakage or spoilage of the product stored inside, or, potentially more seriously, contamination of the container's contents. This is particularly dangerous for products that must be sterile and / or for products containing pharmaceutical substances. Aseptic filling lines, in particular, must be thoroughly cleaned to prevent bacterial growth through spilled filler material and to prevent container contamination.

[0020] Especially during the melting of recycled materials, a phenomenon known as gel formation can occur. This gel formation refers to localized areas within the material where the material does not exist as a free-flowing thermoplastic polymer, but rather undergoes cross-linking due to bridging between molecules. In these cross-linked regions, the material behaves differently during the blow molding process, resulting in localized thick spots. The absence of material accumulated in these thick spots in other areas of the plastic container leads to thin areas, container cracking during blow molding, or even the formation of holes, resulting in container leakage.

[0021] Defects in plastic containers caused by gel formation are a major problem. Gels are known to pass through filters during recycling, or they may form after filters in recycling equipment. In recycled injection molding, gelation is often unavoidable. In technical terms, it is commonly referred to as PET gel, fisheye, or cross-linked PET. Generally, gel formation is said to occur in localized areas of the material where it does not exist as a free-flowing thermoplastic polymer, but rather as cross-linked material due to intermolecular bridging. In these cross-linked regions, the material behaves differently during the blow molding process, resulting in localized thick spots.

[0022] The second category of defects consists of defects caused by unmelted PET. Similar to the aforementioned material thick spots, there is also an accumulation of unmelted PET here, leading to failure at or near the defect. This unmelted PET is usually still easily identifiable as white fine particles or granules within transparent PET. In technical terminology, the terms "unmelted material" or "recrystallization" are frequently used.

[0023] Such unmelted material can also appear after the filter in the recycling unit, for example, due to uneven crystallization or uneven packing of PET, or chemical differences in the type or concentration of comonomers. It can also occur if the material entering the extruder is too cold, or if it absorbs too little shear heat due to the slip effect, and is therefore insufficiently heated.

[0024] The third category consists of genuine contamination caused by foreign substances. These impurities can be, for example, fine glass particles, metal, wood, paper, rubber, or other contaminants. In technical terms, such defects are often referred to as black spots because these impurities caused by foreign substances are usually visible and typically black.

[0025] Therefore, the general term "impurity" refers to all the defects as described above.

[0026] The sources of impurities vary greatly. On the one hand, melt filtration of recycled particles is very prone to failure, and impurities are not filtered out; on the other hand, these defects may also appear later, such as during remelting in the production process of plastic containers. Impurities may also enter the equipment during filter replacement.

[0027] Granules are typically transported in bags, and PET, in particular, generates a very large static charge. This charge causes fine dirt particles to enter the granules.

[0028] It has been found that impurities only cause problems when they exceed a certain size.

[0029] The device for reducing impurities allows impurities to be crushed by the cutting edges on the bridging member, reducing the size of the impurities to a level that would normally no longer cause defects in the blow-molded container.

[0030] A cutting edge is an element that enables the mechanical splitting or separation of a body. A cutting edge is formed by the intersection of two flat or curved surfaces at an acute angle. Their imaginary line of intersection has a radius of 0. This is not possible in practice; instead, the surfaces merge with each other within the radius. This radius is less than 0.2 mm, particularly less than 0.1 mm, and preferably less than 0.05 mm.

[0031] The bridging element preferably has a length in the flow direction and a thickness perpendicular to the flow direction. The length is at least three times, preferably five times, the thickness.

[0032] Therefore, the reduction of impurities here is also understood as the modification of impurities, especially cutting or chopping, because once they are smaller than a certain size, they have little effect on quality and therefore no longer appear as impurities in the process.

[0033] This device can already be used in recycling processes, but it is also suitable for use in injection molding or blow molding processes, especially after the extruder, so that the melt passes through the device as the penultimate step and is injected into the mold or extruded into a tube in the final step.

[0034] The opening of the device preferably has a net diameter of less than 0.8 mm, particularly less than 0.6 mm, and more preferably less than 0.3 mm.

[0035] These dimensions ensure that all fine particles larger than 0.8 mm, 0.6 mm, and 0.3 mm, respectively, remain trapped in the device or are crushed by the cutting edge. If impurities are filtered out, they no longer cause defects. However, if these fine particles are not filtered out but crushed, they are typically so small that they no longer form defects. Crushing is particularly advantageous because the device or its openings will not be blocked.

[0036] The cut edge preferably has a cutting angle of less than 45°. In particular, the cutting angle is less than 35°, and preferably less than 25°. However, preferably, the cutting angle is at least 15°.

[0037] If the angle is less than 15°, there is a risk that the cut edge will break frequently and thus become dull relatively quickly. Additionally, there is a risk that the opening will become clogged relatively quickly at such shallow angles. If the angle is greater than 45°, most structures will no longer be cut correctly and / or relatively high resistance to the melt will occur. A 35° angle achieves relatively good results.

[0038] The device is preferably made of a metallic material. Metals with a melting point above 400°C have proven particularly advantageous. Preferably, the melting point is greater than 800°C.

[0039] This type of metal can be processed using a three-dimensional metal printing process.

[0040] A melting point greater than 800°C allows heat to be used to clean devices clogged or blocked by impurities, i.e., to burn them off.

[0041] The device is typically tubular in shape and has a first open end and a second closed end. This allows the melt to be introduced into the first open end and forced through the closed end and / or sidewalls, and thus filtered accordingly. In this document, the term "filtration" refers to the retention and shredding of impurities.

[0042] Preferably, the device is designed to taper tapering gradually from the first open end to the second closed end. This allows for uniform filtration and, in particular, makes the device easier to clean.

[0043] Openings and, in particular, cut edges are preferably arranged along the entire length of the device. This increases the flow cross-section or passage cross-section.

[0044] The device is preferably arranged within a housing. This arrangement facilitates easy attachment of the device and replacement when necessary.

[0045] On the other hand, an extruder head is disclosed, which includes means for reducing impurities in the plastic melt. The extruder head specifically includes the means as described herein. This means having multiple bridging elements with cutting edges. The means is arranged on the extruder head such that the plastic melt flows through it. This implies flow passage in its intended use.

[0046] Extruder heads with such cutting edges allow for the filtration of the melt after extrusion and before it is introduced into the hot runner system, or for the crushing of impurities contained therein, so that they have no negative impact on the subsequently blown containers, or at least only an acceptable negative impact.

[0047] The device is preferably monitored by one or more pressure sensors that monitor the pressure distribution as the melt flows through it. Specifically, when used for injection molding, the injection pressure is monitored, and if the pressure rises above a defined threshold, such as 10%, the user is instructed to clean the device.

[0048] The device is preferably arranged within a housing, which is preferably rotatably arranged transversely to the flow direction of the molten plastic together with the device. This allows the device to be rotated, causing the flow to pass through it in a direction opposite to the original flow direction. This allows the device to be acted upon from the other side, thus acting against the normal flow direction and flushing the device. Consequently, impurities that cannot be cut off can be easily removed from the device.

[0049] Additionally or alternatively, the device may be pivotally arranged parallel to the longitudinal axis of the extruder head. This arrangement allows the device to be pivoted out of the processing path and cleaned and / or replaced accordingly. The longitudinal axis is typically defined by the flow direction at the end of the extruder head.

[0050] In particular, multiple devices can be provided that can swing into the processing path in the manner of rotating rollers, thereby allowing for continuous replacement. This enables uninterrupted processing or manufacturing.

[0051] On the other hand, it relates to an injection molding machine that includes the apparatus as described herein or the extruder head as described herein. This makes it possible to provide an injection molding machine with coordinated components.

[0052] On the other hand, a blow molding machine is involved, which includes the apparatus as described herein or the extruder head as described herein. This allows for the provision of particularly coordinated components for the blow molding machine.

[0053] On the other hand, a method for reducing impurities in a plastic melt is provided, particularly using an apparatus as described herein. In this method, impurities in the plastic melt are pulverized such that their size is less than 0.8 mm, particularly less than 0.6 mm, and preferably less than 0.3 mm.

[0054] This method provides a plastic melt that contains only impurities, which no longer have a negative impact on the finished blow-molded container.

[0055] In this method, impurities are preferably shredded during the extrusion process using bridging elements with cutting edges arranged in the flow of the plastic melt. This allows for the provision of a high-quality melt with fewer impurities prior to further processing. Attached Figure Description

[0056] The apparatus and method according to the present invention are explained using schematic diagrams. In the drawings:

[0057] Figure 1 A device for reducing impurities is shown;

[0058] Figure 2 It shows Figure 1 Detailed view;

[0059] Figures 3A to 3D : This shows cross-sectional views of different cross sections of the bridging component;

[0060] Figure 4 The crushing process is shown.

[0061] Figure 5 The backwashing process is illustrated.

[0062] Figure 6 The extruder head is shown.

[0063] Figure 7 The following is shown during backwashing. Figure 6 The extruder head. Detailed Implementation

[0064] Figure 1 Device 100 is shown. Device 100 has a first open end 101 and a second open end 102. From the first open end 101 to the second open end 102, device 100 is substantially tapered. Device 100 has a plurality of openings 20, which are formed by bridging members 21 therebetween. This gives device 100 a mesh-like appearance.

[0065] Figure 2 Shown in magnified form Figure 1A detailed view is shown. Multiple openings 20 can be seen, with bridging elements 21 between them. These openings 20 are essentially rhomboid. The net diameter of these openings 20 is determined by incorporating a circle within each opening 20 and defining its diameter. In the present case, the openings 20 shown here have a net diameter of 0.3 mm. In other words, a circle with a diameter of 0.3 mm can be incorporated within the rhomboid openings.

[0066] Figures 3A to 3D It shows along such Figure 2 The line BB shown passes through the cross section of the bridging member 21. Figure 3A A rhomboid bridging member 21 is shown, which has a cut edge 22 at one end. This cut edge 22 is arranged against the flow direction of the molten plastic K, such that impurities V from the molten plastic K impact this cut edge 22. (See later...) Figure 4 The process will be explained in detail. In the current case, the cutting edge 22 has a cutting angle of approximately 33°.

[0067] Figure 3B A cross-section through an alternative embodiment of the bridging member 21 is shown. In this case, the bridging member 21 is lens-shaped and also has a cut edge 22 at at least one end. The tangent of the cut edge 22 has an angle of approximately 36°.

[0068] Figure 3C A cross-section through an alternative embodiment of the bridging member 21 is shown. In this case, the bridging member 21 is triangular and also has a cut edge 22 at at least one end. The cut edge 22 here has an angle of approximately 11°. Although an angle of 11° is below the minimum angle of 15°, it is still a suitable choice for certain plastics.

[0069] Figure 3D A cross-section of another alternative embodiment of the bridging member 21 is shown. In this case, the bridging member 21 is designed as a semi-transparent mirror and also has a cut edge 22 at at least one end. The cut edge 22 here has an angle of approximately 40°.

[0070] For the stability of the bridging member 21, it is particularly advantageous that the length of the bridging member in the flow direction is at least twice the dimension perpendicular to the flow direction.

[0071] Figure 4 The process of crushing impurities V within the plastic melt K is illustrated. As can be seen, multiple bridging elements 21 are arranged adjacent to each other. Each bridging element 21 has a cut edge 22. For clarity, only one bridging element is shown with reference numerals.

[0072] The size ratio is also illustrated using one of the bridge components. As can be seen, this bridge component has a length L and a thickness D. In this example, the length L corresponds to four times the thickness D.

[0073] Impurities V within the molten plastic K impact the cutting edge 22 of the bridging member 21 along the flow direction indicated by the arrow. Therefore, the flowing molten plastic K containing impurities V is pressed against the cutting edge 22 and thus forced through the opening 20 between the bridging members 21 and simultaneously cut. Downstream of the bridging member 21, only impurities V', significantly smaller than those preceding the bridging member 21, remain. The size of these impurities V' no longer negatively impacts subsequent processing steps, such as injection molding or blow molding.

[0074] Figure 5 The backwashing process is illustrated schematically. An injection mold 41 connected to the corresponding extruder head 40 is shown. Within this extruder head 40, a device 100 for reducing impurities in the molten plastic is arranged. Figure 5 As shown above, the device 100 is arranged along the flow direction, enabling it to perform the corresponding filtration effect. Figure 5 As shown below, the extruder head 40 is spaced apart from the injection mold 41, and the device 100 is rotated 180° so that it can be flushed by the subsequent plastic melt in the extruder head 40. Impurities that are not cut out but remain in the device 100 can be flushed out of the device 100, as indicated by the arrows.

[0075] Figure 6 An extruder head 40 is shown, within which a device 100 is arranged. The device 100 is also arranged within a housing 30. The housing 30 is rotatably mounted within the extruder head 40. Figure 6 In this process, the flow direction of the molten plastic is from left to right. Therefore, the molten plastic enters the first opening end 101 (see...). Figure 1 ), and in this process, it is forced to pass through device 100 and is filtered. For example Figure 4 As depicted, various impurities are crushed, but some impurities are still trapped inside the device 100 and gradually clog the device.

[0076] Figure 7 The extruder head 40 is now shown when the device 100 is being cleaned. The housing 30 within the extruder head 40 is arranged against the flow direction along with the device 100, allowing the molten plastic in the extruder head to act against the previous flow direction onto the device 100. This allows impurities that have accumulated in the device 100 to be flushed out. This allows for easy and quick cleaning of the device 100.

Claims

1. An apparatus (100) for reducing impurities (V) in a plastic melt (K), particularly in a thermoplastic material, characterized in that, The device includes a plurality of openings (20) with bridging members (21) between the plurality of openings, wherein cutting edges (22) are formed on the bridging members (21), wherein the cutting edges (22) are arranged against the flow direction of the plastic melt (K) such that the impurities (V) from the plastic melt (K) impact these cutting edges (22) as they flow through the device.

2. The apparatus (100) according to claim 1, characterized in that, The thermoplastic material is a polyester or polyolefin, particularly colored or uncolored PET, copolymers of PET, PEF, HDPE, PP, wherein the material is a virgin material, a recycled material, or a mixture of virgin and recycled materials.

3. The apparatus (100) according to claim 1 or 2, characterized in that, The opening (20) has a net diameter of less than 0.8 mm, particularly less than 0.6 mm, and preferably less than 0.3 mm.

4. The apparatus (100) according to any one of claims 1 to 3, characterized in that, The cutting edge (22) has a cutting angle of less than 45°, particularly less than 35°, and preferably less than 25°, wherein the cutting angle is preferably at least 15°.

5. The apparatus (100) according to any one of claims 1 to 4, characterized in that, The device is made of metal.

6. The apparatus (100) according to any one of claims 1 to 5, characterized in that, The device (100) is tubular and has a first open end (101) and a second closed end (102).

7. The apparatus (100) according to claim 6, characterized in that, The device is designed to taper tapering from the first open end (101) to the second closed end (102).

8. The apparatus (100) according to any one of claims 6 or 7, characterized in that, The opening (20) is arranged along the entire device (100).

9. The apparatus (100) according to any one of claims 1 to 8, characterized in that, The device is arranged in the housing (30).

10. An extruder head (40) comprising means (100) for reducing impurities (V) in a plastic melt (K), particularly the means according to any one of claims 1 to 9, the means having a plurality of bridging members (21) with cutting edges (22), characterized in that, The device (100) is arranged on the extruder head such that the plastic melt (K) flows through the device (100).

11. The extruder head (40) according to claim 10, characterized in that, The device (100) is arranged in a housing (30), wherein the housing (30) and the device (100) are rotatably arranged transversely to the flow direction of the plastic melt (K).

12. The extruder head (40) according to claim 10 or 11, characterized in that, The device (100) is pivotally arranged parallel to the longitudinal axis of the extruder head (40).

13. An injection molding machine comprising the apparatus according to any one of claims 1 to 9 or the extruder head according to any one of claims 10 to 12.

14. A blow molding machine, the blow molding machine comprising the apparatus according to any one of claims 1 to 9 or the extruder head according to any one of claims 10 to 12.

15. A method for reducing impurities (V) in a polymer melt (K), particularly using the apparatus according to any one of claims 1 to 9, characterized in that, The impurities (V) in the polymer melt (K) are crushed so that their size is less than 0.8 mm, particularly less than 0.6 mm, and preferably less than 0.3 mm.

16. The method according to claim 15, characterized in that, The impurities are shredded during the extrusion process by bridging members (21) with cutting edges (22) arranged in the flow of plastic melt (K).

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